Enter Truss Details
Example Data Table
| Item | Example Value | Notes |
|---|---|---|
| Total span | 30 ft | Outside wall to outside wall span. |
| Building length | 40 ft | Length used for truss count and roof area. |
| Pitch | 8 in 12 | Eight inches of rise for each foot of run. |
| Spacing | 24 in | Common layout value for preliminary planning. |
| Attic room width | 14 ft | Width checked against roof slope and knee wall. |
Formula Used
Half span: span ÷ 2.
Roof slope: pitch rise ÷ 12.
Ridge height: half span × roof slope.
Top chord one side: square root of half span squared plus ridge height squared.
Top chord with overhang: square root of adjusted run squared plus adjusted rise squared, then multiplied by two.
Truss count: ceiling of building length ÷ spacing in feet, plus one end truss.
Roof gravity load: roof dead load plus the larger of roof live load or snow load.
Load per truss: roof gravity load × span × truss spacing in feet.
Floor load: attic floor area × total floor load per square foot.
Material estimate: top chords, bottom chords, attic frame members, estimated webs, and waste factor.
How to Use This Calculator
Enter the outside wall span first. Use 30 feet for a standard 30 foot attic truss. Add the building length, pitch, overhang, spacing, and room goals. Then enter roof and attic floor loads from your plan or local requirement. Press Calculate to view the result below the header and above the form. Use CSV or PDF buttons to save the same result.
About the 30 Foot Attic Truss Calculator
A 30 foot attic truss must support the roof and create usable room. This calculator gives a planning view before you talk with a truss designer. It checks span, pitch, overhang, room width, and clear height. It also estimates roof surface, top chord length, truss count, storage floor area, and basic material cost. The tool is helpful for early budgeting. It is not a stamped design.
Why attic truss planning matters
Attic trusses carry roof loads and floor loads at the same time. That makes them different from simple roof trusses. A higher pitch gives more headroom, but it may increase roof area and material length. Wider room space improves storage, but it can reduce web room and change the structural layout. Local snow, wind, and live load rules also matter. Always confirm loads with your building code and supplier.
What the results mean
The ridge height is the rise from the wall line to the roof peak. The top chord length is the sloped distance from eave to ridge, plus overhang. The roof area estimate uses both roof planes. Truss count is based on building length and spacing. Load per truss is an approximate tributary load. It helps compare options, but it does not replace engineered reactions, plate sizes, bearing details, or bracing plans.
Better estimates for materials
Use real project measurements when possible. Measure the outside wall span, not the inside room width. Enter the pitch from drawings or roof plans. Add overhang only when it exists on both sides. Use spacing from your plan, such as sixteen or twenty four inches. Include a waste factor for cuts, blocking, handling damage, and layout changes. Material cost is only a rough length based estimate.
Important safety note
Attic trusses are manufactured structural products. Do not cut, notch, drill, or modify them without written approval. Your final design should come from a licensed engineer or approved truss manufacturer. Use this calculator for planning, comparison, and discussion. Then order trusses with full drawings, bearing sizes, load cases, bracing notes, and code compliance documents.
Keep copies of supplier drawings on site. Inspectors may ask for them during framing when rooms or storage areas are included.
FAQs
What is a 30 foot attic truss?
It is a roof truss designed to span about 30 feet while creating usable attic space inside the truss profile.
Can this calculator replace engineered truss drawings?
No. It gives planning estimates only. Final truss design must be checked by a truss manufacturer, engineer, or approved designer.
Which pitch is best for attic trusses?
A steeper pitch usually gives more headroom. The best pitch depends on roof style, codes, snow load, and room needs.
How is truss count estimated?
The calculator divides building length by spacing in feet. It then adds one extra truss for the end position.
Why does room width affect the fit check?
Wider rooms reach farther down the roof slope. That lowers side height and may conflict with the selected knee wall height.
Are overhangs included in the top chord length?
Yes. The top chord estimate includes both side overhangs when an overhang value is entered in the form.
What loads should I enter?
Use loads from local code, project plans, or your designer. Snow, wind, storage, and live loads vary by location.
Can I cut an attic truss after delivery?
No. Do not cut or alter any truss unless the manufacturer or engineer gives written repair or modification instructions.